This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to a Japanese Patent Appllcauon 2002-005065, filed on Jan. 11, 2002, the entire content of which is incorporated herein by reference.
This invention generally relates to a vehicle traveling control system for controlling a vehicle speed at an upper threshold speed or smaller than that. More particularly, this invention pertains to a vehicle traveling control system for controlling a vehicle speed by applying braking force during driving force being applied in a state where the vehicle is slowly traveling.
There have been various technologies conventionally known, in which a vehicle speed is controlled within a predetermined speed range while the vehicle is traveling. For example, an auto-cruising system has been conventionally known, in which a predetermined vehicle speed can be obtained by automatically adjusting an opening degree of a throttle valve while the vehicle is traveling within a relatively high-speed range.
On the other hand, a Japanese Patent Laid-Open No. 10(1998)-278825 discloses a technology for controlling a vehicle speed while a vehicle is slowly traveling at a slow-speed, in which the vehicle is automatically parked while it is traveling utilizing a creep force. In general, the vehicle speed is controlled in response to operation of a brake pedal by a vehicle driver. However, according to the above-disclosed technology, the brake pedal operation is properly carried out when the driver is alerted by an alerting unit that the actual vehicle speed has exceeded an intended vehicle speed range for performing the automatic parking. There has been other technology conventionally known, in which the vehicle speed is controlled by applying braking force to a vehicle wheel when the actual vehicle speed exceeds a predetermined threshold speed value, wherein the automatic parking can be properly performed.
While the vehicle is creeping, it is preferable to improve a vehicle speed controlling performance and to expand a vehicle speed control range. Torque-up operation has been conventionally known to increase driving force to be applied to the vehicle wheel so as to achieve the above-described objectives. However, requisite braking force under the torque-up operation is increased comparing with the requisite braking force when the torque-up operation has not been performed. Therefore, according to the aforementioned conventional technology, a vehicle braking system may be applied with greater load and the brake operating amount by the driver may be increased.
The present invention therefore seeks to provide an improved vehicle traveling control system capable of controlling the applied driving force without increasing the load applied to the braking system.
A vehicle traveling control system of the present invention includes a control mode for controlling a vehicle speed by applying braking force so as to maintain the vehicle speed at a predetermined upper threshold vehicle speed or smaller than that while a predetermined driving force beyond a creeping torque has been applied. The applied driving force is reduced when a braking force (a target braking force or an actual braking force) required for maintaining the vehicle speed at the predetermined upper threshold vehicle speed or smaller than that is equal to a first predetermined value or greater than that. Therefore, the load to a braking system or to a driver can be effectively reduced.
The applied driving force is increased when the target braking force or the actual braking force becomes a second predetermined value or smaller than that during the applied driving force being reduced. The second predetermined speed value is preset to be smaller than the first predetermined value. Therefore, the sufficient torque can be applied to a vehicle engine and a hunting condition of torque up and down operation can be restrained, wherein the driving condition is prevented from being deteriorated.
The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawing figures wherein:
FIG. 1 is a block view illustrating a vehicle traveling control system according to an embodiment of the present invention;
FIG. 2 illustrates a flow chart for explaining an upper threshold vehicle speed maintaining process by the vehicle traveling control system illustrated in FIG. 1; and
FIG. 3 is a time chart showing a result of the upper threshold vehicle speed maintaining process illustrated in FIG. 2 as an example.